Full movie description "The Avengers Two's a Crowd":

A mysterious Russian called Psev is arriving for a conference at which Steed and Mrs. Peel have been hired to act as the security guards. However, a man called Gordon Webster who is an exact double for Steed turns up and offers his services to Psev's entourage of four people, fooling Mrs. Peel in the process and agreeing to kill Steed. Though he is thwarted it turns out that Psev is also not exactly the man that everybody had expected him to be.

Film Review

"Two's a Crowd" is a rare disappointment, marred by weak villains and an inconsistent tone. Steed heads up security for an important conference, hoping to snare the elusive Colonel Psev, who has escaped detection for years because he's never been properly identified. The Colonel's circle of agents torment Ambassador Vladimir Jiroslav Brodny (Warren Mitchell, who would repeat the characterization in "The See-Through Man"), until they spot a male model who looks exactly like Steed, only without the scruples. It doesn't take long for them to convince the unpolished double to replace the real Steed, and start by convincing Mrs. Peel that he can actually pass for the real thing. Alas, the hapless Brodny can't hold a candle to Nigel Stock's Zalenko, Steed's friendly enemy from "Concerto," but once he fades into the background, things improve considerably, especially with Patrick Macnee's solid dual performance (he always complements his fellow actors). Warren Mitchell was already a series veteran ("The Golden Fleece" and "The Charmers"), but newcomer Julian Glover proved to be one of its most dependable villains, returning for "The Living Dead," "Split!" and "Pandora." Other veterans back again included Wolfe Morris ("The Yellow Needle" and "The Decapod") and Alec Mango ("Conspiracy of Silence"), but there was little difference between Psev's villains, the one major weakness of a mostly solid plot line.